1. Field of the invention:
The present invention relates to a drive coupling device for use in optical instruments which are detachably combined together. The drive coupling device of the present invention is used, for example, for transmitting a drive force from a camera body as one optical instrument to a lens shifting mechanism in an interchangeable lens as another optical instrument for automatic focusing, when the interchangeable lens is mounted on the camera body.
2. Description of the Prior Art:
Drive coupling devices for optical instruments are required to be connected or disconnected automatically and reliably at the same time that the optical instruments incorporating such drive coupling devices are coupled to or detached from each other. Such drive coupling devices are disclosed in Japanese Laid-Open Utility Model Publication No. 57-9914 (hereinafter referred to as Publication (1)), Japanese Laid-Open Patent Publications Nos. 57-173809, 57-177105, and 57-195224 (hereinafter referred to as Publications (2), (3), (4), respectively), for example. In these disclosed drive coupling devices, generally, the drive coupling member in one optical instrument extends parallel to the optical axis thereof, and the driven coupling member in another optical instrument also extends parallel to the optical axis thereof. These drive and driven coupling members are connected through a male-and-female interfitting connection to each other to couple the optical instruments together.
The drive coupling device shown in Publication (1) has a male engaging portion in the form of a cross screwdriver tip, and a female engaging portion in the form of a cross-recessed screw head, the male and female engaging portions being interfittingly engageable with each other. The drive coupling device shown in the Publications (2), (3), (4) includes a flat male engaging portion and a slotted female engaging portion which can be brought into mesh with each other. The flat male and slotted female engaging portions illustrated in Publication (2) also have central female and male centering engaging portions, respectively.
The drive coupling device shown in Publication (1) is advantageous in that the male and female engaging portions can easily be interfitted and disengaged, and when in mesh with each other, they can center the drive and driven coupling members coaxially with each other. The drive coupling device is also advantageous in that the male and female engaging portions are automatically engaged and disengaged smoothly with and from each other by relative movement of the two optical instruments in a direction perpendicular to the axes of the drive and driven coupling members. These advantages are achieved by the male and female engaging portions held in contact with each other through slanted surfaces. However, when a rotative drive force is to be transmitted between the drive and driven coupling members, the male and female engaging portions are subject to a force tending to disengage them out of meshing relation due to the contact at their slanted surfaces. Thus, no stable torque transmission is achieved, and high torques cannot be transmitted by the drive and driven coupling device
With the drive coupling device shown in Publications (3), (4), the male and female engaging portions are not subject to a force which would tend to disengage them in transmitting the rotative drive force. As a consequence, the disclosed drive coupling device can essentially stably transmit torques and can transmit high torques. However, the drive coupling device of this type has a disadvantage described below.
FIGS. 10 and 11 of the accompanying drawings illustrate such drive coupling device composed of a driven coupling member B in an optical instrument A and a drive coupling member D in an optical instrument C. The optical instruments A, C as combined together may not be positionally aligned or may have the driven and drive coupling members B, D disposed out of alignment. Therefore, when the optical instruments A,C are coupled together, the flat male engaging portion d and the slotted female engaging potion b may be in mesh with each other with their axes E, F out of alignment, as shown in FIGS. 10 and 11. The illustrated drive coupling device has no ability to correct such an axial misalignment. The rotative drive force is transmitted while the flat male engaging portion d and the slotted female engaging portion b are out of axial alignment, with the result that the male and female engaging portions d, b are liable to get distorted or twisted. Further, the male engaging portion d tends to rub against the inner peripheral surface of an axial receiving bore G, damaging the inner peripheral surface thereof and allowing chips from the damaged inner peripheral surface to enter between the inner peripheral surface and the outer peripheral surface of the driven coupling member B. The illustrated prior drive coupling device is therefore of a low torque transmission efficiency, has low durability, and is apt to produce noises, actually. When the drive force is transmitted from the flat male engaging portion d to the slotted female engaging portion b, the flat male engaging portion d contacts an edge b' of the slotted female engaging portion b as shown in FIG. 11. The edge b' is subject to a concentrated shock-induced stress and may be damaged thereby as when the drive coupling member D is abruptly stopped. For the above reason, the drive coupling device is less durable, and the damages make the drive coupling device poor in appearance. To eliminate the above shortcomings, the slotted female engaging portion b would have to be formed in a relatively large size.
The drive coupling device of Publication (2) transmits torques in the same manner as those of Publications (3) and (4), and has central male and female engaging portions for preventing the male and female coupling members from being misaligned during a rotation. Therefore, it is free from the disadvantages which would arise from the torque transmission by the misaligned drive and driven coupling members. However, the construction is more complex due to the "double-engaging" structure and costly to manufacture. Moreover, the male and female engaging portions have no ability to guide the male and female coupling members for centering their axes when the axes are misaligned beyond a certain degree so as not to allow engagement of the central male engaging portion into the central female engaging portion.